1. Technical Field
Several aspects of the present invention relate to a semiconductor device, a method for manufacturing the same, and an electro optical device.
2. Related Art
In recent years, flexible electronic apparatuses have increasingly attracted attention. A flexible display typified by electronic paper, for example, is not only light to carry with, but also shock absorbing and foldable by hand, and can be the electronic apparatus to help realization of the ubiquitous network society. Proposed in JP-T-2003-518756, for example, is such an electronic apparatus having bendable organic thin film transistors (hereunder abbreviated as organic TFTs) mounted thereon.
Because the transistor elements of the organic TFTs are fabricated at normal temperature and pressure, the production costs can be low. The production costs can even be greatly reduced by using such general printing techniques as an inkjet technique and a spin coating technique.
However, because a field effect transfer rate of an organic TFT is several digits lower than that of a TFT using a silicon thin film, if all the TFTs in an electronic device are organic, the drive capacity of the device is reduced. To solve this problem, the organic TFTs may be used only partially in the device, and other semiconductor elements with higher field effect transfer rates may be used for the drive circuit.
Among them, low-temperature polysilicon thin film transistors (hereunder abbreviated as LTPS-TFTs) are suited to solve the problem. Because of its high field effect transfer rate, the drive capability of the LTPS-TFTs is not reduced even when an area of the electronic device occupied by the LTPS-TFTs is small, and, therefore, the LTPS-TFTs are suitable for reducing the size of the device in weight and thickness. However, a disadvantage is that the LTPS-TFTs need to be manufactured at a temperature as high as 600° C. and are not easily fabricated on a plastic substrate used for a flexible device.
This disadvantage is solved by a mounting technique referred to as surface-free technology by laser ablation/annealing (SUFTLA: a registered trademark of Seiko Epson Corp.), in which the LTPS-TFTFs are fabricated on a glass substrate in advance and then transferred onto a plastic substrate. JP-A-2003-297974 is an example of the related art.
In the manufacture of a semiconductor device having the organic TFTs, however, if the organic TFTs are first fabricated on the flexible substrate, they become readily damaged as they are vulnerable to heat and moisture. More specifically, in the process of SUFTLA for transferring peripheral circuits, the LTPS-TFTs are thermally compressed on the flexible substrate with an adhesive agent. Thus, the high temperature and pressure applied to the transistor elements of the organic TFTs may deteriorate the performance of the transistor elements.